In the operation of a fluid system serving a plurality of parallel work elements, the work elements sometimes demand large volumes of fluid from their associated hydraulic fluid pump. Occasionally there arise situations where the work elements demand fluid at a rate greater than the capacity of the pump. In such situations, one or more of the work elements will be demanding more fluid than is available while another work element may be requiring fluid at a very high pressure in order to continue to function under its existing load. Since the fluid passing to the work elements is free to travel the path of least resistance, the above-mentioned work elements demanding additional fluid will be supplied the required fluid at the expense of denying the increased pressure demanded by said other work element.
This problem associated with a plurality of work elements connected in parallel can be avoided by providing a pump having a capacity greater than the total demand capacity that could ever be required by the work elements. However, to so construct the work vehicle would produce a waste of materials, time, and labor for constructing, maintaining, and handling the resultant large pump. Further, the undesirably large pump would add considerable extra weight to the vehicle and would require extra fuel to operate which would further represent a waste of energy.
It is therefore desirable to provide fluid system apparatus which will control the system in a manner such that when the work elements approach a total fluid demand exceeding the capacity of the associated fluid pump, the actual demands of the work elements will be automatically overridden in response to a load pressure signal and fluid delivery to the individual work elements will be automatically, controllably maintained at reduced rates relative to their individual actual demand.
This invention therefore resides in controlling the fluid delivered to individual parallel work elements in response to a load pressure signal and the total fluid demand of the work elements relative to the maximum capacity or the pumps.